Thursday, December 29, 2016

Origin-Destination Flow Maps

Earlier this month I read an interesting article in the Cartography and Geographic Information Science journal, examining Design Principles for Origin-Destination Flow Maps. In the paper the authors suggest three good design principles for visualizing origin-destination flows where specific routes between the origin and destination are unknown or unimportant.

One of the three design principles suggested in the article is that "curved flows are more effective than straight flows". A good example of this design principle can be seen in practice in Bostongraphy's Hubway Trip Explorer. In this interactive map Bostongraphy has mapped trips taken on Boston's bike share network.

The map allows you to explore trips taken on the network by time of day, day of the week, month of the year, in different weather conditions and by the gender & age of the rider. Once you have used these options to filter the data the origin-destination flows are then visualized on a map of Boston using curved flow lines.

The use of these curved lines to show the origin-destination flows on the map seems much more effective than assigning specific routes (for example by using the shortest route between the origin & destination), The use of wider curves for longer distances ensures that the individual origin-destination flows can be clearly differentiated on the map. If straight line routes between the individual bike stations had been used instead of these curved line flows the individual origin-destination flows would be much harder to read on the map. It probably also wouldn't have been as aesthetically pleasing as this rather beautiful looking map of the traffic flows between Boston's Hubway stations.